This application relates to networks composed of local area networks (LANs) connected by LAN bridges.
A LAN is a network of computing systems (generally referred to as end systems) which are connected by a common communications medium, or bus. Messages are transferred from one end system to another via the LAN by conveying the message, along with the address of the intended recipient end system, onto the common communications bus. Each end system then receives the message and reads the address. If the message address matches the recipient end system""s address, the message is processed; otherwise, the message is discarded. Thus, in a LAN, every message is received by every end system; this allows for simple interconnection and rapid communication, but limits the number of end systems that can be effectively interconnected.
When the number of end systems on a LAN becomes unmanageable, or when geographical restrictions prohibit serviceable connection of all end systems on a single LAN, system managers typically organize groups of end systems into several LANs, and use bridges to provide connections between the LANS, forming a LAN/bridge network.
In one aspect, the invention features a bridge for simultaneous connection to n LANs, where n is greater than 2. The bridge includes storage for respectively associating the (n2xe2x88x92n)/2 unique pairs of LANs connected by the bridge with (n2xe2x88x92n)/2 parallel bridge numbers. Messages received from a first LAN are forwarded to a second LAN only if the message identifies the second LAN and the parallel bridge number which is associated in the storage with the first and second LANs.
In another aspect, the invention features a method for determining whether two or more ports of a bridge having three or more ports are connected to the same LAN. The bridge attempts to transmit messages from each port of the bridge to each other respective port of the bridge by addressing the messages to the data link addresses of the other ports. After transmission, the bridge waits a short time interval and determines whether any of the messages are received at any of its ports. If a message is received at a port, then the port receiving the message and the port which transmitted the message must be connected to the same LAN.
Preferred embodiments include the following features.
When a set of two or more ports are determined to be connected to the same LAN, all ports in the set may be disabled, and the bridge may issue a warning of a fault. Or, if desired, one of the ports in the set may be selected for use, and the other ports disabled. If the ports are identified by numbers, the port with the numerically highest or lowest number can be selected for use; alternatively, the port with the highest capacity can be selected, but if two ports of the set have the same capacity, the port with the numerically highest or lowest number can be selected.
In another aspect, the invention features a method of determining whether a port of a bridge connected to a token ring LAN is properly sending and receiving messages. A message is sent from the port to itself by sending the message, via the token ring, to the port""s own data link address. If the message is not received by the port during a short time interval after transmission, then there is a fault in the port. If desired, a warning of the fault can then be issued.